Hydraulic brake apparatus for a vehicle

ABSTRACT

A hydraulic brake apparatus for a vehicle includes a supplementary hydraulic pressure source outputting a pressurized output hydraulic pressure and an electronic control apparatus that controls a hydraulic pump in the supplementary hydraulic pressure source. The electronic control apparatus judges whether the hydraulic pump satisfies a predetermined operating condition based on the output hydraulic pressure of the supplementary hydraulic pressure source or not. The electronic control apparatus compares the output hydraulic pressure with a minimum standard hydraulic pressure, detects a drop in the output hydraulic pressure when the output hydraulic pressure is less than a standard hydraulic pressure and determines that the hydraulic pump does not satisfy the predetermined operating condition.

[0001] This application is based on and claims priority under 35 U.S.C.§119 with respect to Japanese Patent Application 2000-261929, filed onAug. 30, 2000, the entire content of which is incorporated herein byreference.

FIELD OF THE INVENTION

[0002] This invention generally relates to a hydraulic brake apparatusfor a vehicle. More particularly, the present invention pertains to ahydraulic brake apparatus for the vehicle having an auxiliary hydraulicpressure source for generating a power hydraulic pressure to be used toapply brake pressure to a wheel cylinder associated with a wheel of thevehicle in response to operation of a brake operating member, and awarning mechanism for informing of a failure of an outputted hydraulicpressure generated by the auxiliary hydraulic pressure source.

BACKGROUND OF THE INVENTION

[0003] Various types of hydraulic brake apparatus for a vehicle areknown. At least some known types of hydraulic brake apparatus include amaster cylinder such as a hydraulic pressure generating apparatus forgenerating a brake pressure in response to operation of a brakeoperating member, and an auxiliary hydraulic pressure source forgenerating a power hydraulic pressure. The auxiliary hydraulic pressuresource generally includes a hydraulic pump and an accumulator. Thesehydraulic brake apparatus typically require an adjustment of the powerhydraulic pressure generated by the auxiliary hydraulic pressure sourceand an adequate warning in response to an excessive reduction of the thepower hydraulic pressure.

[0004] For example, U.S. Pat. No. 5,000,520 (corresponding to a JapanesePatent Application published on May 24, 1990 as Toku-Kai-Hei 2(1990)-136365) discloses a hydraulic brake apparatus in which the powerhydraulic pressure varies between 140-180 bar under operation of theauxiliary hydraulic pressure source. The pumping operation of ahydraulic pump is started in response to the reduction of the powerhydraulic pressure below a predetermined lower limit and is continueduntil the power hydraulic pressure reaches an upper limit. A warningsignal is generated in response to the reduction of the power hydraulicpressure below a predetermined lowest limit set at 105 bar.

[0005] In the apparatus disclosed in the above-mentioned U.S. patent, tooperate the hydraulic pump and generate the warning signal when a relaycontact fails, an electric circuit arrangement is provided that includesa pressure responsive switch and a relay arrangement for controllingoperation of an electric driving motor connected to the hydraulic pumpto maintain the power hydraulic pressure within a predetermined range(e.g. 140-180 bar), another pressure responsive switch for generatingthe warning signal in response to the reduction of the power hydraulicpressure below the predetermined lower limit, and another relay forcontrolling the operation of the electric driving motor.

[0006] In the apparatus described in the above-mentioned U.S. patent, ifthe hydraulic pump is normally operable, it is able to maintain adriving condition of the hydraulic pump in response to a reduction ofthe power hydraulic pressure. However, if the capacity of theaccumulator is small, the warning signal may be frequently generatedduring normal operation of the hydraulic pump. Further, the electriccircuit arrangement including the two pressure responsive switches andthe two relays increases the manufacturing cost associated with theapparatus.

[0007] A need thus exists for a hydraulic brake apparatus having anauxiliary hydraulic pressure source for generating a power hydraulicpressure in which, if the hydraulic pump is normally operating, theoperation of the hydraulic pump is controlled in response to varying thepower hydraulic pressure to generate the power hydraulic pressurewithout generating frequent warning signals.

SUMMARY OF THE INVENTION

[0008] According to one aspect of the present invention, a hydraulicbrake apparatus for a vehicle includes a reservoir containing brakefluid, a wheel cylinder associated with a road wheel of the vehicle, andan auxiliary hydraulic pressure source for generating a power hydraulicpressure that is used to apply brake pressure to the wheel cylinder inresponse to a braking requirement. The auxiliary hydraulic pressuresource includes a hydraulic pump for increasing the pressure of thebrake fluid supplied from the reservoir to generate the power hydraulicpressure. A power hydraulic pressure observing device observescontinuously the power hydraulic pressure and generates a signal forcontrolling operation of the hydraulic pump based on the power hydraulicpressure. A pump operating condition judging mechanism judges whether ornot the operating condition of the hydraulic pump satisfies apredetermined operating condition based on the power hydraulic pressureobserved by the power hydraulic pressure observing means. A warningmechanism compares the power hydraulic pressure observed by the powerhydraulic observing device with a predetermined hydraulic pressure andgenerates a warning signal indicating a failure of the power hydraulicpressure when the power hydraulic pressure is less than thepredetermined hydraulic pressure and the pump operating conditionjudging mechanism judges that the operating condition of the hydraulicpump does not satisfy with the predetermined operating condition.

[0009] The pump operating condition judging mechanism detects a risingtendency of the power hydraulic pressure observed by the power hydraulicpressure observing device, and the pump operating condition judgingmechanism judges that the operationg condition of the hydraulic pumpsatisfies the predetermined operating condition when the power hydraulicpressure observed by the power hydraulic pressure observing device showsthe rising tendency while the power hydraulic pressure observed by thepower hydraulic pressure observing device is less than the predeterminedhydraulic pressure.

[0010] The pump operating condition judging mechanism detects a risingtendency of the power hydraulic pressure observed by the power hydraulicpressure observing device and detects the starting of driving of thehydraulic pump, and the pump operating condition judging means judgesthat the operating condition of the hydraulic pump satisfies thepredetermined operating condition when the power hydraulic pressureobserved by the power hydraulic pressure observing device shows therising tendency from a zero pressure within a predetermined time periodafter the driving of the hydraulic pump is started.

[0011] The pump operating condition judging mechanism detects a risingtendency of the power hydraulic pressure observed by the power hydraulicpressure observing device, and the pump operating condition judgingmechanism judges that the operating condition of the hydraulic pumpsatisfies the predetermined operating condition when the power hydraulicpressure observed by the power hydraulic pressure observing device showsthe rising tendency within the predetermined time period after the powerhydraulic pressure observed by the power hydraulic pressure observingdevice falls below the predetermined hydraulic pressure.

[0012] The pump operating condition judging mechanism calculates achanging rate of the power hydraulic pressure observed by the powerhydraulic pressure observing device and detects a starting of a drivingof the hydraulic pump, and the pump operating condition judgingmechanism judges that the operating condition of the hydraulic pumpsatisfies the predetermined operating condition when the changing rateof the power hydraulic pressure observed by the power hydraulic pressureobserving device becomes a positive rate within a predetermined timeperiod after the driving of the hydraulic pump is started.

[0013] The pump operating condition judging mechanism calculates achanging rate of the power hydraulic pressure observed by the powerhydraulic pressure observing device, and the pump operating conditionjudging mechanism judges that the operating condition of the hydraulicpump satisfies the predetermined operating condition when the changingrate of the power hydraulic pressure observed by the power hydraulicpressure observing device changes from a negative rate to a positiverate within a predetermined time period after the power hydraulicpressure observed by the power hydraulic pressure observing device fallsbelow the predetermined hydraulic pressure.

[0014] The hydraulic brake apparatus also includes a hydraulic pressuregenerating apparatus for generating the brake pressure in response tooperation of a brake operating member. The hydraulic pressure generatingapparatus includes a master cylinder and a hydraulic brake boosteroperable by the power hydraulic pressure to assist in operation of themaster cylinder. A master cylinder hydraulic pressure sensor is providedto continuously detect the master cylinder hydraulic pressure generatedby the master cylinder. A consumed hydraulic pressure estimatingmechanism is provided for estimating a consumed hydraulic pressure atthe auxiliary hydraulic pressure source based on the master cylinderpressure detected by the master cylinder hydraulic pressure sensor. Thepump operating condition judging mechanism calculates a changing rate ofthe power hydraulic pressure observed by the power hydraulic pressureobserving device and calculates a changing rate of the consumedhydraulic pressure estimated by the consumed hydraulic pressureestimating mechanism. The pump operating condition judging mechanismjudges that the operating condition of the hydraulic pump satisfies thepredetermined operating condition when a sum of the changing rate of theconsumed hydraulic pressure estimated by the consumed hydraulic pressureestimating mechanism and a predetermined lowest changing rate of theoutputting hydraulic pressure of the hydraulic pump is less than thechanging rate of the power hydraulic pressure observed by the powerhydraulic pressure observing device.

[0015] The hydraulic brake apparatus further includes a wheel cylinderhydraulic pressure sensor for detecting continuously the hydraulic brakepressure supplied to the wheel cylinder, a consumed hydraulic pressureestimating mechanism for estimating a consumed hydraulic pressure at theauxiliary hydraulic pressure source based on the wheel cylinderhydraulic detected by the wheel cylinder hydraulic pressure sensor. Thepump operating condition judging mechanism calculates a changing rate ofthe power hydraulic pressure observed by the power hydraulic pressureobserving device and calculates a changing rate of the consumedhydraulic pressure estimated by the consumed hydraulic pressureestimating mechanism. The pump operating condition judging mechanismjudges that the operating condition of the hydraulic pump satisfies thepredetermined operating condition when a sum of the changing rate of theconsumed hydraulic pressure estimated by the consumed hydraulic pressureestimating mechanism and a predetermined lowest changing rate of theoutputting hydraulic pressure of the hydraulic pump is less than thechanging rate of the power hydraulic pressure observed by the powerhydraulic pressure observing device.

[0016] According to another aspect of the present invention, a hydraulicbrake apparatus for a vehicle includes a reservoir containing brakefluid, a wheel cylinder associated with a road wheel of the vehicle, andan auxiliary hydraulic pressure source for generating a power hydraulicpressure used to apply a brake pressure to the wheel cylinder inresponse to a braking requirement. The auxiliary hydraulic pressuresource includes a hydraulic pump for increasing a pressure of the brakefluid supplied from the reservoir to generate the power hydraulicpressure. A power hydraulic pressure monitoring mechanism detectscontinuously the power hydraulic pressure and generates a signal forcontrolling operation of the hydraulic pump based on a detected powerhydraulic pressure. A mechanism detects a changing rate of the powerhydraulic pressure detected by the power hydraulic pressure monitoringmechanism, and generates a warning signal indicating a failure of thepower hydraulic pressure on the basis of the detected power hydraulicpressure and the changing rate of the detected power hydraulic pressure.

[0017] According to another aspect of the invention, a method ofoperating a vehicle hydraulic brake apparatus involves continuouslydetermining a power hydraulic pressure generated by an auxiliaryhydraulic pressure source, wherein the auxiliary hydraulic pressuresource includes a hydraulic pump which increases a pressure of brakefluid supplied from a reservoir to generate the power hydraulic pressurethat is used to apply brake pressure to a vehicle wheel cylinder. Asignal is generated to control operation of the hydraulic pump based onthe power hydraulic pressure, and the power hydraulic pressure generatedby the auxiliary hydraulic pressure source is compared with apredetermined hydraulic pressure of the auxiliary hydraulic pressuresource. A determination is made regarding whether or not an operatingcondition of the hydraulic pump satisfies a predetermined operatingcondition based on the detected power hydraulic pressure, and a warningis issued indicating failure of the power hydraulic pressure when thedetected power hydraulic pressure is less than the predeterminedhydraulic pressure and when it is determined that the operatingcondition of the hydraulic pump does not satisfy the predeterminedoperating condition.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0018] The foregoing and additional features and characteristics of thehydraulic brake apparatus for a vehicle according to the presentinvention will become more apparent from the following detaileddescription considered in conjunction with the accompanying drawingfigures in which like elements bear like reference numerals and wherein:

[0019]FIG. 1 is a schematic block diagram of a hydraulic brake apparatusaccording to a first embodiment of a present invention;

[0020]FIG. 2 is a graph showing characteristics of a hydraulic pumpbased on accumulator pressure according to the first embodiment of thepresent invention;

[0021]FIG. 3 is a block diagrams showing a construction of an electroniccontrol apparatus according to the first embodiment of the presentinvention;

[0022]FIG. 4 is a flowchart of a main routine including the driving ofthe hydraulic pump and the warning process performed by the CPUaccording to the first embodiment of the present invention;

[0023]FIG. 5 is a flowchart of a pump operating condition judgmentaccording to the first embodiment of the present invention;

[0024]FIG. 6 is a flowchart of a pump operating condition judgmentaccording to a second embodiment of the present invention;

[0025]FIG. 7 is a graph showing a first characteristic of theaccumulator pressure according to the first embodiment of the presentinvention;

[0026]FIG. 8 is a graph showing a second characteristic of theaccumulator pressure according to the first embodiment of the presentinvention; and

[0027]FIG. 9 is a graph showing a third characteristic of theaccumulator pressure according to the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Referring initially to FIG. 1 which schematically illustrates theconstruction of a hydraulic brake apparatus according to an embodimentof the present invention, the vehicle hydraulic brake apparatus includesa hydraulic pressure generating apparatus PG that increases the pressureof brake fluid supplied from a brake fluid containing reservoir RV inresponse to operation of a brake operating member such as a brake pedalBP and supplies brake pressure to a wheel cylinder WC. The vehiclehydraulic brake apparatus also includes an auxiliary hydraulic pressuresource AP for generating a power hydraulic pressure.

[0029] The auxiliary hydraulic pressure source AP includes a hydraulicpump FP driven by an electric motor M. The hydraulic pump FP has aninlet hydraulically connected a brake fluid containing reservoir and anoutlet hydraulically connected to an accumulator AC through a checkvalve CV.

[0030] A hydraulic pressure sensor PS1 is connected to the accumulatorAC. The accumulator pressure of the power hydraulic pressure generatedby the auxiliary hydraulic pressure source AP is continuously detectedby the hydraulic pressure sensor PS1, and is observed or monitored by apower hydraulic pressure observing or monitoring means PM based on theoutput from the hydraulic pressure sensor PS1. The motor M for drivingthe hydraulic pump FP is controlled by a motor driving control means MCbased on the hydraulic pressure detected by the hydraulic pressuresensor PS1 as observed by the power hydraulic pressure observing meansPM. More specifically, as shown in FIG. 2, when the accumulator pressuredecreases below a lower level Pn (a predetermined lower limit), thedriving of the electric motor M is started. When the accumulatorpressure increases to an upper level (a predetermined upper limit) Pf,the driving of the electric motor M is stopped.

[0031] A pump operating condition judging means CD judges whether or notthe operation of the hydraulic pump FP satisfies a predeterminedoperating condition at least on the basis of the accumulator pressure orthe power hydraulic pressure of the auxiliary hydraulic pressure sourceAP observed by the power hydraulic pressure observing means PM. The boldsolid line in FIG. 2 shows the relationship between the accumulatorpressure and the amount of stored brake fluid in the accumulator ACunder operation of the auxiliary hydraulic pressure source.

[0032] The pump operating condition judging means CD is constructed suchthat the pump operating condition judging means CD judges or determinesthat the operation of the hydraulic pump FP satisfies the predeterminedoperating condition when the accumulator pressure (i.e., the powerhydraulic pressure) generated by the auxiliary hydraulic pressure sourceAP and observed by the power hydraulic pressure observing means PM showsa rising tendency while the accumulator pressure observed by the powerhydraulic pressure observing means PM is less than a predeterminedlowest hydraulic pressure Pw (predetermined hydraulic pressure).

[0033] Alternatively, as shown in FIG. 7, the pump operating conditionjudging means CD may be constructed such that the pump operatingcondition judging means CD judges or determines that the operation ofthe hydraulic pump FP satisfies the predetermined operating conditionwhen the accumulator pressure pressure (i.e., the power hydraulicpressure) generated by the auxiliary hydraulic pressure source AP andobserved by the power hydraulic pressure observing means PM shows arising tendency from a zero pressure within a predetermined time periodafter the driving of the hydraulic pump FP is started.

[0034] As a further alternative shown in FIG. 8, the pump operatingcondition judging means CD may be constructed such that the pumpoperating condition judging means CD judges or determines that theoperating condition of the hydraulic pump FP satisfies the predeterminedoperating condition when the accumulator pressure pressure (i.e., thepower hydraulic pressure) generated by the auxiliary hydraulic pressuresource AP and observed by the power hydraulic pressure observing meansPM shows a rising tendency within a predetermined time period after theaccumulator pressure observed by the power hydraulic pressure observingmeans PM falls below the predetermined lowest hydraulic pressure Pw(predetermined hydraulic pressure).

[0035] A warning means WR compares the accumulator pressure (i.e., thepower hydraulic pressure) generated by the auxiliary hydraulic pressuresource AP and observed by the power hydraulic pressure observing meansPM with the predetermined lowest hydraulic pressure Pw. Only when theaccumulator accumulator pressure is less than the predetermined lowesthydraulic pressure Pw and the pump operating condition judging means CDjudges or determines that the operating condition of the hydraulic pumpFP does not satisfy the predetermined operating condition, the warningmeans WR generates a warning signal informing or advising of a failureof the accumulator pressure generated by the auxiliary hydraulicpressure source AP. The warning means WR can take a variety of forms,including a warning lamp or a warning buzzer, and is operable inresponse to the warning signal as an informing device which informs thedriver of the vehicle of the failure of the accumulator pressure. Also,it is to be understood that the warning signal generated by the warningmeans WR may be supplied to another brake control apparatus such as ananti-skid control apparatus.

[0036] The above-mentioned hydraulic pressure generating apparatus PGmay be comprised of a master cylinder MC and a hydraulic brake boosteroperable by the power hydraulic pressure generated by the auxiliaryhydraulic pressure source AP to assist operation of the master cylinderMC. As shown in phantom lines in FIG. 1, several additional features canbe incorporated into the hydraulic brake apparatus. That is, thehydraulic brake apparatus can be provided with a master cylinderhydraulic pressure sensor PS2 for detecting the output hydraulicpressure of the master cylinder MC continuously, and a consumedhydraulic pressure estimating means CP for estimating the consumedhydraulic pressure of the auxiliary hydraulic pressure source AP basedon the pressure detected by the master cylinder hydraulic pressuresensor PS2. The pump operating condition judging means CD calculates thechanging rate of the accumulator pressure observed by the powerhydraulic pressure observing means PM and detects the starting of thedriving of the hydraulic pump FP. The consumed hydraulic pressureestimating means CP calculates a changing rate of the consumed hydraulicpressure at the auxiliary hydraulic pressure source AP estimated by theconsumed hydraulic pressure estimating means CP. The pump operatingcondition judging means CD judges that the operating condition of thehydraulic pump FP satisfies the predetermined condition when the sum ofthe changing rate of the consumed hydraulic pressure of the auxiliaryhydraulic pressure source AP estimated by the consumed hydraulicpressure estimating means CP and a predetermined lowest changing rate ofthe outputted hydraulic pressure of the hydraulic pump FP is less than achanging rate of the accumulator pressure observed by the powerhydraulic pressure observing means PM. This point is explained belowfurther with reference to FIGS. 6 and 9.

[0037] As also shown in FIG. 1, the hydraulic brake apparatus can alsobe provided with a wheel cylinder hydraulic pressure sensor PS3 forcontinuously detecting the hydraulic pressure of the wheel cylinder WC.The consumed hydraulic pressure estimating means CP estimates theconsumed hydraulic pressure at the supplementary hydraulic pressuresource AP based on the wheel cylinder hydraulic pressure detected by thehydraulic pressure sensor PS3. The pump operating condition judgingmeans CD performs a judgment similar to the above-mentioned condition.

[0038] As shown in FIG. 3, an electronic control apparatus CT includes amicrocomputer CM which can perform the function of, for example, theabove-mentioned output hydraulic pressure observing means PM. Thehydraulic pressure sensor PS1, the master cylinder hydraulic pressuresensor PS2, and the wheel cylinder hydraulic pressure sensor PS3 areconnected to the electronic control apparatus CT so that the electroniccontrol apparatus CT receives input from these sensors. The electroniccontrol apparatus CT controls the operation of the electric motor M andthe informing device in the warning means WR.

[0039] In FIG. 3. the electronic control apparatus CT includes themicrocomputer CM including a CPU, a ROM, a RAM, an input interface IT,and an output interface OT which are connected via a bus. Output signalsfrom the hydraulic pressure sensors PS1, PS2, PS3 are transmitted fromthe input interface IT to the CPU via amplifier circuits AI. Further,control signals outputted from the microcomputer CM through the outputinterface OT are transmitted to to the electric motor M and theinforming device in the warning means WR via driving circuits AO. In themicrocomputer CM, the ROM stores a program corresponding to theflowchart shown in FIG. 4, the CPU executes the program while anignition switch of the vehicle is in the ON condition, and the RAMtemporarily stores needed variable data when the program is executed.

[0040] In the hydraulic brake apparatus having the above-mentionedconstruction, the electronic control apparatus CT executes a series ofprocesses or steps to effect driving control of the hydraulic pump FPand warning indication by the warning means WR. When the ignition switchis in the closed condition (i.e., when the ignition is started), thestored program in the ROM is started by the microcomputer CM. Thewarning process of the warning means WR based on the flowchart in FIG. 4is executed as explained below.

[0041] Referring to the program or routine shown in FIG. 4, at step 101the microcomputer CM performs an initialization in which variouscalculated values are cleared. Next, the program proceeds to step 102 inwhich the output signal of the hydraulic pressure sensor PS1 (i.e., theaccumulator pressure Pa which is the output hydraulic pressure of theauxiliary hydraulic pressure source AP) is read by the CPU. At step 103,the accumulator pressure Pa is compared to the lower level pressure Pnwhich is a standard or set value indicating when the driving of thehydraulic pump FP is started. When the accumulator pressure Pa is lessthan the lower level pressure Pn, the program proceeds to step 104 atwhich the hydraulic pump FP is driven by the motor M. Next, the programproceeds to step 105 where the accumulator pressure Pa is compared tothe lowest hydraulic pressure or predetermined hydraulic pressure Pw(Pw<Pn). When the CPU determines at step 105 that the accumulatorpressure Pa is less than the lowest hydraulic pressure Pw, the programproceeds to step 106. Here the CPU judges whether or not the operatingcondition of the hydraulic pump FP satisfies the predetermined operatingcondition. When it is determined in step 106 that the operatingcondition of the hydraulic pump FP satisfies the predetermined operatingcondition, the program returns to step 102. When the operating conditionof the hydraulic pump FP does not satisfy the predetermined operatingcondition in step 106, the program advances to step 107 and a warning isemitted by the warning means WR.

[0042] The determination in step 106 of FIG. 4 regarding whether or notthe operating condition of the hydraulic pump FP satisfies thepredetermined operating condition is carried out according to theflowchart shown in FIG. 5. Initially in step 201 of FIG. 5, the CPUjudges whether or not the accumulator pressure Pa is less than thelowest hydraulic pressure Pw. For example, as shown in FIG. 7, as theaccumulator pressure Pa falls to a zero pressure when the vehicle isplaced in a condition of long time parking so that the accumulatorpressure Pa is lost, the accumulator pressure Pa is necessarily lessthan the lowest hydraulic pressure Pw. Under a condition such as whenthe accumulator pressure Pa is zero, the program proceeds to step 202when the driving of the hydraulic pump FP is started after the ignitionswitch is closed (i.e., when the ignition is turned on). Here, a counterfor a timer T starts at step 202. Then, the CPU judges at step 203whether or not a change in the accumulator pressure exhibits a risingtendency from the zero condition within a predetermined time Tk. In thisembodiment, the CPU judges at step 203 whether or not a differentialvalue (dPa/dt) of the accumulator pressure Pa is greater than zero. Whenthe differential value (i.e., the changing rate) dPa/dt is greater thanzero, the CPU judges that the operation of the hydraulic pump FP isnormal and the operationg condition of the hydraulic pump FP satisfiesthe predetermined operating condition. Then, the program proceeds tostep 204 at which a pump condition flag Fp is set to 1.

[0043] On the other hand, when the differential value dPa/dt of theaccumulator pressure Pa is less than zero and the accumulator pressurePa does not exhibit a rising tendency at step 203, the program proceedsto step 205 where the CPU judges whether or not the count value of thetimer T has passed a predetermined time Tk. When the CPU judges at step206 that the count value of the timer T is equal to or less than thepredetermined time Tk, the program returns to the main routine shown inFIG. 4. However, when the CPU judges at step 205 that the count value ofthe timer T is greater than the predetermined time Tk, the CPUdetermines that it is not satisfied with the operating condition of thehydraulic pump FP because the accumulator pressure Pa does not show arise tendency within the predetermined time Tk. Therefore, the programproceeds to step 206 where the pump condition flag Fp is cleared tozero.

[0044] On the other hand, when for example the accumulator pressure Pais excessively consumed by normal braking and/or automatic braking(e.g., steering control by braking, traction control, etc.) so that theaccumulator pressure Pa falls below the lowest hydraulic pressure Pw,the program proceeds from step 201 to step 202 in FIG. 5, and the timerT is counted up at step 202. Next, the CPU judges whether or not theaccumulator pressure Pa shows a rising tendency within the predeterminedtime Tk. That is, the CPU judges at step 203 whether the differentialvalue dPa/dt of the accumulator pressure Pa changes from a negativevalue to a positive value. When the accumulator pressure Pa exhibits therising tendency as shown in FIG. 8, the differential value dPa/dtchanges to a positive value and so the CPU judges that the operatingcondition of the hydraulic pump FP satisfies the predeterminedcondition. The program then proceeds to step 204 where the pumpcondition flag Fp is set to 1. When the accumulator pressure Pa does notexhibit the rising tendency at step 203, the program proceeds to step205.

[0045] At step 205, the CPU judges whether or not the count value of thetimer T is within the predetermined time Tk. When the CPU judges thatthe count value of the timer T has passed or exceeded the predeterminedtime Tk at step 205, the program proceeds to step 206. Here, the pumpcondition flag Fp is cleared (i.e., set to zero).

[0046]FIG. 6 shows an alternative routine for judging whether or not theoperating condition of the hydraulic pump FP satisfies the predeterminedoperating condition at step 106 in FIG. 4. In step 301, the CPUinitially judges whether or not the normal braking operation or theautomatic braking operation (e.g., steering control by braking, tractioncontrol, etc.) is occurring, namely whether the accumulator pressure isbeing consumed. If it is determined in step 301 that normal braking orautomatic braking is operating, the program proceeds to step 302. Atstep 302, the consumed hydraulic pressure P1 at the accumulator AC isestimated based on the master cylinder hydraulic pressure detected bythe master cylinder hydraulic pressure sensor PS2 at step 302. That is,the amount of consumed hydraulic fluid at a hydraulic pressure circuitincluding all wheel cylinders is estimated based on the master cylinderpressure, and then the amount of consumed hydraulic fluid at theaccumulator AC is estimated based on the amount of consumed hydraulicfluid of the hydraulic pressure circuit. The consumed hydraulic pressureat the auxiliary hydraulic pressure source AP (i.e., the consumedhydraulic pressure P1 of the accumulator AC) is estimated according tothe graph shown in FIG. 2.

[0047] The program then proceeds to step 303 at which the gradient ofthe consumed hydraulic pressure P1 at the accumulator AC (i.e., thechanging rate of the consumed hydraulic pressure at the accumulator AC)is calculated by the CPU. The sum of the changing rate ΔP1 of theconsumed hydraulic pressure at the accumulator AC and a predeterminedlowest changing rate ΔPp of the outputting hydraulic pressure of thehydraulic pump FP (corresponding to ΔPe in FIG. 9 ) is compared to achanging rate ΔP0 of the power hydraulic pressure (accumulator pressurePa) of the auxiliary hydraulic pressure source AP observed by the powerhydraulic pressure observing means PM. FIG. 9 shows the relationshipbetween ΔP0, ΔP1, ΔPp, ΔPe and the accumulator pressure Pa. Further, thelowest changing rate ΔPp of the outputting hydraulic pressure of thehydraulic pump FP means a changing rate of the outputting hydraulicpressure of the pump FP (a constant value) when the environmentcondition is set to the worst condition for the output of the hydraulicpump FP, e.g., when the voltage of the motor M is a lower value and thecircumference temperature is a lower value.

[0048] Further, at step 303, the CPU judges or determines that theoperating condition of the hydraulic pump FP satisfies the predeterminedoperating condition when the CPU determines that the changing rate ΔP0of the accumulator pressure Pa is equal to or greater than the sum ofthe changing rate ΔP1 of the consumed hydraulic pressure at theaccumulator AC and the predetermined lowest changing rate ΔPp of theoutputting hydraulic pressure of the hydraulic pump FP (ΔP0≧ΔP1+ΔPp ).In other words, when the above-mentioned sum (ΔP1+ΔPp) is less than thechanging rate ΔP0 of the accumulator pressure Pa, the program proceedsto step 304 where the pump condition flag Fp is set to 1. To thecontrary, when the changing rate ΔP0 of the accumulator pressure Pa isless than the above-mentioned sum (ΔP1+ΔPp), in other words theabove-mentioned sum (ΔP1+ΔPp) is greater than the changing rate ΔP0 ofthe accumulator pressure Pa, the program proceeds to step 305 where thepump condition flag is cleared or set to zero.

[0049] It is to be understood that the consumed hydraulic pressure P1 ofthe accumulator AC can also be estimated based on the wheel cylinderpressure detected by the hydraulic pressure sensor PS3 of the wheelcylinder WC shown in FIG. 1. Further, the CPU can be adapted todetermine or judge the pump operating condition by another method suchas the above-mentioned determining method based on the consumedhydraulic pressure P1 at the accumulator AC. It is thus possible toprevent an unnecessary warning when the automatic brake control isoperating.

What is claimed is:
 1. A hydraulic brake apparatus for a vehiclecomprising: a reservoir containing brake fluid; a wheel cylinderoperatively associated with a road wheel of the vehicle; an auxiliaryhydraulic pressure source for generating a power hydraulic pressure usedto apply brake pressure to the wheel cylinder in response to a brakingrequirement, the auxiliary hydraulic pressure source including ahydraulic pump for increasing a pressure of the brake fluid suppliedfrom the reservoir to generate the power hydraulic pressure; powerhydraulic pressure observing means for continuously observing the powerhydraulic pressure generated by the auxiliary hydraulic pressure sourceand for generating a signal to control operation of the hydraulic pumpbased on the power hydraulic pressure; pump operating condition judgingmeans for judging whether or not an operating condition of the hydraulicpump satisfies a predetermined operating condition based on the powerhydraulic pressure observed by the power hydraulic pressure observingmeans; and warning means for comparing the power hydraulic pressureobserved by the power hydraulic observing means with a predeterminedhydraulic pressure and for generating a warning signal indicating afailure of the power hydraulic pressure when the power hydraulicpressure is less than the predetermined hydraulic pressure and the pumpoperating condition determining means determines that the operatingcondition of the hydraulic pump does not satisfy the predeterminedoperating condition.
 2. The hydraulic brake apparatus according to claim1, wherein the pump operating condition judging means detects a risingtendency of the power hydraulic pressure observed by the power hydraulicpressure observing means, and the pump operating condition judging meansjudges that the operating condition of the hydraulic pump satisfies thepredetermined operating condition when the power hydraulic pressureobserved by the power hydraulic pressure observing means shows a risingtendency while the power hydraulic pressure observed by the powerhydraulic pressure observing means is less than the predeterminedhydraulic pressure.
 3. The hydraulic brake apparatus according to claim2, wherein the pump operating condition judging means judges a risingtendency of the power hydraulic pressure observed by the power hydraulicpressure observing means and detects a starting of a driving of thehydraulic pump, and the pump operating condition judging means judgesthat the operating condition of the hydraulic pump satisfies thepredetermined operating condition when the power hydraulic pressureobserved by the power hydraulic pressure observing means shows therising tendency from a zero pressure within a predetermined time periodafter the driving of the hydraulic pump is started.
 4. The hydraulicbrake apparatus according to claim 2, wherein the pump operatingcondition judging means judges a rising tendency of the power hydraulicpressure observed by the power hydraulic pressure observing means, andthe pump operating condition judging means judges that the operatingcondition of the hydraulic pump satisfies the predetermined operatingcondition when the power hydraulic pressure observed by the powerhydraulic pressure observing means shows the rising tendency within thepredetermined time period after the power hydraulic pressure observed bythe power hydraulic pressure observing means falls below thepredetermined hydraulic pressure.
 5. The hydraulic brake apparatusaccording to claim 1, further comprising: a hydraulic pressuregenerating apparatus for generating brake pressure in response tooperation of a brake operating member, the hydraulic pressure generatingapparatus including a master cylinder and a hydraulic brake boosteroperable by the power hydraulic pressure to assist operation of themaster cylinder; a master cylinder hydraulic pressure sensor forcontinuously detecting a master cylinder hydraulic pressure generated bythe master cylinder; a consumed hydraulic pressure estimating means forestimating consumed hydraulic pressure at the auxiliary hydraulicpressure source based on the master cylinder pressure detected by themaster cylinder hydraulic pressure sensor; and the pump operatingcondition judging means calculating a changing rate of the powerhydraulic pressure observed by the power hydraulic pressure observingmeans and calculating a changing rate of the consumed hydraulic pressureestimated by the consumed hydraulic pressure estimating means, the pumpoperating condition judging means judging that the operating conditionof the hydraulic pump satisfies the predetermined operating conditionwhen a sum of the changing rate of the consumed hydraulic pressureestimated by the consumed hydraulic pressure estimating means and apredetermined lowest changing rate of the outputting hydraulic pressureof the hydraulic pump is less than the changing rate of the powerhydraulic pressure observed by the power hydraulic pressure observingmeans.
 6. The hydraulic brake apparatus according to claim 1, furthercomprising: a wheel cylinder hydraulic pressure sensor for continuouslydetecting the hydraulic brake pressure supplied to the wheel cylinder; aconsumed hydraulic pressure estimating means for estimating consumedhydraulic pressure at the auxiliary hydraulic pressure source based onthe wheel cylinder hydraulic pressure detected by the wheel cylinderhydraulic pressure sensor; and the pump operating condition judgingmeans calculating a changing rate of the power hydraulic pressureobserved by the power hydraulic pressure observing means and calculatinga changing rate of the consumed hydraulic pressure estimated by theconsumed hydraulic pressure estimating means, the pump operatingcondition judging means judging that the operating condition of thehydraulic pump satisfies the predetermined operating condition when asum of the changing rate of the consumed hydraulic pressure estimated bythe consumed hydraulic pressure estimating means and a predeterminedlowest changing rate of the outputting hydraulic pressure of thehydraulic pump is less than the changing rate of the power hydraulicpressure observed by the power hydraulic pressure observing means. 7.The hydraulic brake apparatus according to claim 1, wherein the pumpoperating condition judging means calculates a changing rate of thepower hydraulic pressure observed by the power hydraulic pressureobserving means and detects a starting of driving of the hydraulic pump,and the pump operating condition judging means judges that the operatingcondition of the hydraulic pump satisfies the predetermined operatingcondition when the changing rate of the power hydraulic pressureobserved by the power hydraulic pressure observing means becomespositive within a predetermined time period after the driving of thehydraulic pump is started.
 8. The hydraulic brake apparatus according toclaim 4, wherein the pump operating condition judging means calculates achanging rate of the power hydraulic pressure observed by the powerhydraulic pressure observing means, and the pump operating conditionjudging means judges that the operating condition of the hydraulic pumpsatisfies the predetermined operating condition when the changing rateof the power hydraulic pressure observed by the power hydraulic pressureobserving means changes from a negative rate to a positive rate within apredetermined time period after the power hydraulic pressure observed bythe power hydraulic pressure observing means falls below thepredetermined hydraulic pressure.
 9. A hydraulic brake apparatus for avehicle comprising: a reservoir containing brake fluid; a wheel cylinderassociated with a road wheel of the vehicle; an auxiliary hydraulicpressure source for generating a power hydraulic pressure used to applya brake pressure to the wheel cylinder in response to a brakingrequirement, the auxiliary hydraulic pressure source including ahydraulic pump for increasing a pressure of the brake fluid suppliedfrom the reservoir to generate the power hydraulic pressure; powerhydraulic pressure monitoring means for continuously detecting the powerhydraulic pressure generated by the auxiliary hydraulic pressure sourceand for generating a signal to control operation of the hydraulic pumpbased on the detected power hydraulic pressure; means for detecting achanging rate of the power hydraulic pressure detected by the powerhydraulic pressure monitoring means and for generating a warning signalindicating a failure of the power hydraulic pressure on the basis of thedetected power hydraulic pressure and the changing rate of the detectedpower hydraulic pressure.
 10. The hydraulic brake apparatus according toclaim 9, wherein said means for detecting a changing rate of the powerhydraulic pressure judges that an operating condition of the hydraulicpump satisfies a predetermined operating condition when a positivechanging rate of the power hydraulic pressure is detected within apredetermined time while the power hydraulic pressure detected by thepower hydraulic pressure monitoring means is less than a predeterminedhydraulic pressure.
 11. The hydraulic brake apparatus according to claim9, wherein the means for detecting a changing rate of the powerhydraulic pressure judges that an operating condition of the hydraulicpump satisfies a predetermined operating condition when a positivechanging rate of the power hydraulic pressure from a zero pressure isdetected by the means for detecting a changing rate of the powerhydraulic pressure detects within a predetermined time period afterdriving of the hydraulic pump is started.
 12. The hydraulic brakeapparatus according to claim 9, wherein the means for detecting achanging rate of the power hydraulic pressure judges that an operatingcondition of the hydraulic pump satisfies a predetermined operatingcondition when a positive changing rate of the power hydraulic pressureis detected by the means for detecting a changing rate of the powerhydraulic pressure within a predetermined time period after the powerhydraulic pressure detected by the power hydraulic pressure monitoringmeans falls below a predetermined hydraulic pressure.
 13. The hydraulicbrake apparatus according to claim 9, further comprising: a hydraulicpressure generating apparatus for generating brake pressure in responseto operation of a brake operating member, the hydraulic pressuregenerating apparatus including a master cylinder and a hydraulic brakebooster operable by the power hydraulic pressure to assist operation ofthe master cylinder; a master cylinder hydraulic pressure sensor forcontinuously detecting a master cylinder hydraulic pressure generated bythe master cylinder; a consumed hydraulic pressure estimating means forestimating consumed hydraulic pressure at the auxiliary hydraulicpressure source based on the master cylinder pressure detected by themaster cylinder hydraulic pressure sensor; and the means for detecting achanging rate of the power hydraulic pressure calculating a changingrate of the consumed hydraulic pressure estimated by the consumedhydraulic pressure estimating means and judging that an operatingcondition of the hydraulic pump satisfies a predetermined operatingcondition when a sum of the changing rate of the consumed hydraulicpressure estimated by the consumed hydraulic pressure estimating meansand a predetermined lowest changing rate of the outputting hydraulicpressure of the hydraulic pump is less than the changing rate of thepower hydraulic pressure detected by the means for detecting a changingrate of the power hydraulic pressure.
 14. The hydraulic brake apparatusaccording to claim 9, further comprising: a wheel cylinder hydraulicpressure sensor for continuously detecting the hydraulic brake pressuresupplied to the wheel cylinder; a consumed hydraulic pressure estimatingmeans for estimating consumed hydraulic pressure at the auxiliaryhydraulic pressure source based on the wheel cylinder hydraulic pressuredetected by the wheel cylinder hydraulic pressure sensor; and the meansfor detecting a changing rate of the power hydraulic pressurecalculating a changing rate of the consumed hydraulic pressure estimatedby the consumed hydraulic pressure estimating means and judging that anoperating condition of the hydraulic pump satisfies the predeterminedoperating condition when a sum of the changing rate of the consumedhydraulic pressure estimated by the consumed hydraulic pressureestimating means and a predetermined lowest changing rate of theoutputting hydraulic pressure of the hydraulic pump is less than thechanging rate of the power hydraulic pressure detected by the means fordetecting a changing rate of the power hydraulic pressure.
 15. A methodof operating a vehicle hydraulic brake apparatus comprising:continuously determining a power hydraulic pressure generated by anauxiliary hydraulic pressure source, the auxiliary hydraulic pressuresource including a hydraulic pump which increases a pressure of brakefluid supplied from a reservoir to generate the power hydraulic pressurethat is used to apply brake pressure to a vehicle wheel cylinder;generating a signal to control operation of the hydraulic pump based onthe power hydraulic pressure; comparing the power hydraulic pressuregenerated by the auxiliary hydraulic pressure source with apredetermined hydraulic pressure of the auxiliary hydraulic pressuresource; determining whether or not an operating condition of thehydraulic pump satisfies a predetermined operating condition based onthe detected power hydraulic pressure; and issuing a warning indicatingfailure of the power hydraulic pressure when the detected powerhydraulic pressure is less than the predetermined hydraulic pressure andwhen it is determined that the operating condition of the hydraulic pumpdoes not satisfy the predetermined operating condition.
 16. The methodaccording to claim 15, including determining a changing rate of thedetected power hydraulic pressure, and judging that the operatingcondition of the hydraulic pump satisfies the predetermined operatingcondition when the changing rate of the detected power hydraulicpressure is positive.
 17. The method according to claim 15, includingdetermining a changing rate of the detected power hydraulic pressure anddetecting starting of driving of the hydraulic pump, and judging thatthe operating condition of the hydraulic pump satisfies thepredetermined operating condition when the changing rate of the detectedpower hydraulic pressure is positive within a predetermined time periodafter the driving of the hydraulic pump is started.
 18. The methodaccording to claim 15, including determining a changing rate of thedetected power hydraulic pressure, and judging that the operatingcondition of the hydraulic pump satisfies the predetermined operatingcondition when the changing rate of the detected power hydraulicpressure is positive within a predetermined time period after the powerhydraulic pressure falls below the predetermined hydraulic pressure.